Flash chemistry based on high-resolution reaction time control using flow microreactors enables chemical reactions that cannot be done in batch and serves as a powerful tool for laboratory synthesis of organic compounds and for production in chemical and pharmaceutical industries.

Rapid mixing to race past rearrangement: Chemistry relies on encounters between reactive partners. Sometimes one of the partners changes shape during the wait, spoiling the desired outcome. Kim et al. designed a microfluidic device to keep such botched encounters from happening. The device operates at low temperatures to keep individual reactants from isomerizing. It also achieves fast flow rates to maximize encounters between reactants on a microsecond time scale. The authors showcase the device by achieving bimolecular carbon-carbon coupling before one of the reagents can undergo a Fries rearrangement that would shift a neighboring group to the coupling site. Science , this issue p. 691